1. Field of the Invention
This invention relates to a process for preparing powdered metal-based iron alloys, from mixed metal iron oxides by treatment with calcium as a reducing agent. The alloys are useful as Fischer-Tropsch catalysts for preparing hydrocarbons from CO and H.sub.2.
2. Brief Discussion of the Prior Art
Calcium metal is known in the art, particularly in steelmaking, as being a strong reducing agent and has the ability to reduce many metal oxides to their respective metals. However, in powdered metal alloy formation, hydrogen gas is usually preferred as the reducing agent due to its ease of handling and also in view of the disadvantages associated with handling metallic calcium.
A general route used to prepare a number of powdered metal alloys consists of heating a mixture of at least two metallic components at temperatures in excess of 1500.degree. C., i.e. above the melting point of either of the two elements. In some cases, mixed metal oxides, which are normally prepared by heating the component oxides, carbonates, or hydroxides, at temperatures near 100.degree. C., and contain two or more different metal ions in close atomic proximity (about 10 .ANG.), are easily reduced in hydrogen to an alloy at low temperatures (about 500.degree. C.), since each oxide component itself reduces easily. This proves true in the case of Fe-Co oxides or Fe-Ni oxides for example. However, with other mixed metal oxides, such as Fe-Cr, Fe-Mn, Fe-Ti, and Fe-Zn types, high temperature (1000.degree. C.) hydrogen reduction reduces either partially or all of the iron to iron metal leaving as a residue an oxide component, and does not generally result in substantially pure alloy as a product.
U.S. Pat. No. 4,373,947 describes a process for producing powdered titanium-based alloys from the calcium reduction of calcined mixture of titanium oxide and a second metal oxide. However, the disclosure does not suggest or teach the applicability of this type of process for preparing iron-based alloys from single phase mixed metal iron oxides.
What is desired in the art is an alternate method for effectively preparing powdered metal-based iron alloys directly by reduction of the corresponding mixed metal iron oxides, particularly where one of the mixed metal oxides is difficulty reducible, and where the reduction can be conducted at a lower temperature than the melting points of the respective metals or mixed metal oxide.